This invention generally relates to apparatus and methods for testing flexible containers. More specifically, this invention relates to apparatus and methods for testing the fluid tightness and/or seal integrity of containers and especially, but not exclusively, is intended for use in testing containers comprising a container body having an aperture or opening which is sealed by a lid or cap.
In many industries, it is important to test the fluid tightness and seal integrity of containers. For example, in the food industry, it is essential to ensure that containers in which food products are packed are completely sealed to ensure that the contents are in good condition, free from molds, bacteria and other pathogenic organisms, so that they will be safe when used by consumers. The pharmaceutical industry similarly requires that containers for medications, especially solutions intended for injection or intravenous administration, be protected from contamination or serious danger to public health may result.
Because fluid tightness and seal integrity of containers is not readily ascertained by visual inspection, various attempts have been made to provide apparatus for testing for these properties (hereinafter, for convenience, called xe2x80x9cleak detection apparatus.xe2x80x9d) For example, U.S. Pat. No. 4,862,732 describes a xe2x80x9csqueezing apparatusxe2x80x9d for testing the fluid tightness and/or seal integrity of plastic bottles, such as those in which laundry detergents are commonly sold. This apparatus creates a pressure within the bottle by squeezing it by means of a pneumatic cylinder. It monitors the position of the piston of this cylinder; if the bottle does not leak, the piston stops as soon as the pressure in the bottle increases enough to balance the force of the piston. After equilibrium, continued pressure caused by the squeezing diminishes as pressurized gas within the bottle leaks by being forced through a leak hole, and thus the piston of the pneumatic cylinder moves further than in the case of a non-leaking bottle.
The apparatus described in this patent gives good results under commercial conditions with the bottles for which it was designed.
U.S. Pat. No. 5,767,392 to William David Belcher, et al. issued on Jun. 16, 1998 describes a method and apparatus for leak testing a closed container by applying a compressive force to the container, releasing the compressive force, and measuring the recovery of the container a predetermined time after the compressive force is released. The recovery is correlated with the pressure or absence of leaks. The Belcher, et al. patent appears to suffer from the inability to cope with variations in container temperature and physical properties of the container and its contents.
Several forms of leak detection apparatus are known which do not rely on squeezing the container. In one form of such apparatus, the container to be tested is placed within a fluid tight chamber, the pressure within the chamber is changed from atmospheric to above or below atmospheric, and the effect of this pressure change on the container is monitored. For example, U.S. Pat. No. 3,751,972 (Hass) describes a leak detector for testing sealed containers formed of semi-rigid or flexible material. The container to be tested is placed in a chamber which is thereafter pressurized at a pressure distinctly different from the internal container pressure, whereby the container is caused to physically distort. A container dimension is first sensed before the chamber is pressurized to produce a first signal representing the dimension resulting from the difference between container internal pressure and atmospheric pressure, this first signal being held. When the container is under pressure in the chamber and a predetermined time interval has elapsed, the container dimension is again sensed to produce a second signal representing the dimension as a result of the difference between internal pressure and chamber pressure. The first held signal and the second signal are compared and if the disparity therebetween indicates a significant change in dimension, the container is accepted, whereas if there is little disparity between the signals, the container is rejected.
Similarly, U.S. Pat. No. 5,105,654 (Maruyama et al.) describes an apparatus which is generally similar to that of Hass but in which at least a portion of the container being tested comprises an electrically conductive material, and the chamber is provided with an eddy-current displacement sensor to detect the position of the conductive material of the container.
U.S. Pat. No. 5,365,774 (Horlacher) also describes an apparatus which is generally similar to that of Hass but in which the chamber is equipped with a suction cup at the end of a suction pipe. This suction cup is placed above the flexible cover of the container being tested. When the pressure in the chamber is reduced, the cover bulges and blocks the suction cup. If the seal between the cover and the body of the container is ineffective, the lid does not bulge and block the cup, thus enabling the ineffective seal to be detected.
U.S. Pat. No. 5,513,516 (Stauffer) describes a method and apparatus in which a flexible or semi-flexible package is received within a closeable test cavity, and a pressure differential is established between the inside of the container and an enclosed space within the test cavity outside of the container. The closeable test cavity comprises a flexible wall whose shape adapts to the shape of the container, at least when the pressure differential is established. The flexible wall advantageously compensates for variations in head space and shape of the packages, as when the contents are not uniformly distributed within the package. The flexible wall can sealingly contact a portion of the container spaced from a container seal to permit detection of seal leaks. A gas permeable, flexible screen can be employed between the container and the flexible wall to permit leak detection of leaks in the container beneath the flexible wall.
Similarly, U.S. Pat. No. 4,055,984 (Marx) describes a device for detecting leaks in an article having readily deformable walls. This device has conventional arrangements for performing a leak detection by overpressure or by vacuum and has a deformable backup wall for engagement with the walls of the article. The backup wall is, on its face oriented towards the article, so configured that between the backup wall and the article there is obtained a coherent fluid tight space which may be evacuated.
The leak detection devices just described suffer from one serious problem when used in commercial settings. Food packages for retail sale, and similar relatively low cost packages, are normally filled on continuous packing lines which run at high speeds, typically at least 30 packages per minute, and it is highly desirable to conduct the leak detection procedure in-line with the packing line. Removing one or two packages from such a packing line, placing them within a vacuum chamber, resealing and applying a vacuum to the chamber, effecting the desired measurement on the package(s), restoring the chamber pressure to atmospheric, opening the chamber and removing the package(s) will in total take at least several seconds. Thus, it is difficult to carry out the leak detection procedure with a throughput sufficient to keep up with the packing line. Although multiple sets of leak detection apparatus can of course be used with a single packing line, the provision of such multiple sets, together with the necessary apparatus for directing packages to the proper leak detection apparatus, and reassembling the packages into a single stream after leak detection, greatly increases the complexity and cost of the packing line.
U.S. Pat. No. 4,774,830 (Hulsman, assigned to the same assignee as the present application), describes a leak detection apparatus which operates on a rather different principle from those previously described. The Hulsman apparatus is used in detecting defective flange-shaped seals between lid and body portions of a package. A pressure chamber is provided for isolating the external edge of the seal and applying a test pressure thereto. Containment of the pressure chamber includes sealing pressure applied mechanically to the flange-shaped package seal during testing. If the seal is defective, gas flows in one direction between the pressure chamber and interior of the package, thus causing a displacement of the lid of the package, and this displacement of the lid is detected by a position detector disposed adjacent a central portion of the lid, this central portion of the lid lying outside the pressure chamber and thus being maintained at ambient pressure. The Hulsman apparatus is effective in detecting leaks and better adapted than the apparatus previously discussed for use in-line with a packing line, since the Hulsman apparatus does not require removal of each package from the line and placement of the whole container within a pressure or vacuum chamber. The pressure chamber of the Hulsman apparatus is formed by two separate members which can close, clamshell style, on a package which is already resting on a transport conveyor or similar device. However, the Hulsman apparatus does require that the seal be placed within a pressure chamber. In addition, there is some risk of mechanical damage as a fragile lid is grasped between the members forming the pressure. Also, the process will not detect a leak located anywhere except in the lid sealing area, for example, in the lid or in the cup.
Accordingly, it is a primary object of the present invention to provide high-speed apparatus and methods for leak testing containers without removing the containers from a production line.
It is another object of the present invention to provide apparatus and methods for in-line leak testing of flexible containers while automatically compensating for container to container variations in temperature and physical properties.
It is another object of the present invention to provide apparatus and method in-line testing of containers for the presence of overfilled, underfilled, and empty containers.
It is another object of the present invention to provide apparatus and methods in-line leak testing of containers which contain self diagnostic capability for detecting changes in apparatus properties such as sensor degradation or drift.
It is yet another object of the present invention to provide apparatus and methods for in-line testing of containers while generating statistical data for process control and quality assurance purposes.
It is yet another object of the present invention to provide apparatus and methods for in-line testing of containers having the ability to keep track of production line stops.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter when the description to follow is read in conjunction with the drawings.
This invention relates to an apparatus for testing flexible containers, this apparatus comprising:
in-line means for applying a predetermined compression over a predetermined time to a plurality of containers as they travel along a production line without interrupting the flow of containers along the production line;
at least two sensors spaced apart with respect to one another at predetermined positions along the path of travel taken by the compressed containers to generate responses that vary in accordance with the internal pressure of the containers as they pass by the sensors; and
means for receiving the responses and analyzing them for the presence of leaks in the containers.
This invention also relates to a method for testing flexible containers as they travel along a production line without interrupting the flow of containers along the production line, this method comprising:
applying a predetermined compression to the plurality of containers as they travel along the production line;
while the predetermined compression is applied to each container, contacting the container with each of at least two sensors spaced apart from one another to generate responses that vary in accordance with the internal pressure of the container at it passes by the sensors, any given container contacting the at least two sensors at different times; and
analyzing the responses for the presence of leaks in the containers.
The apparatus and method of the present invention are useful for in-line testing for leaks in flexible containers traveling along a production line at high speeds. The apparatus can inspect semi-rigid plastic containers at a higher capacity than existing intermittent motion leak detection designs by using multiple sensors positioned at predetermined spaced locations along a compression section to sense properties of the containers as they pass by the sensing stations. The compression of the containers and the location and properties of the sensors are arranged such that the responses of the sensors vary in correspondence with the presence and absence of leaks in the containers. Analysis of the sensor responses is performed to determine which containers have leaks based on differences in responses among the sensors.